A wireless communication device configured for multi-carrier operation can receive data from and/or transmit data to more than one serving cell. Multi-carrier operation may be interchangeably referred to as “carrier aggregation,” “multi-carrier system,” “multi-cell operation,” “multi-carrier transmission,” and/or “multi-carrier reception.” Multi-carrier operation can be configured for transmission of signalling and/or data in the uplink direction, the downlink direction, or both.
In multi-carrier operation, an individual carrier may be referred to as a component carrier, and each serving cell may have an associated component carrier. One of the component carriers is the primary component carrier, PCC, which may be interchangeably referred to as the primary carrier or anchor carrier. The PCC's serving cell is interchangeably called the primary cell, PCell, or primary serving cell, PSC. The remaining component carriers are called secondary component carriers, SCCs, which may be interchangeably referred to as secondary carriers or supplementary carriers. The SCC's serving cell is interchangeably called a secondary cell, SCell, or a secondary serving cell, SSC.
Generally the primary carrier carries the essential signalling that is specific to the wireless communication device. The primary carrier exists in both the uplink and downlink directions. Thus, if there is only a single uplink component carrier, the PCell is on that component carrier. The network may assign different primary carriers to different wireless communication devices operating in the same sector or cell.
A network node uses a multi-carrier SCell setup procedure to at least temporarily setup or release an SCell for a wireless communication device capable of multi-carrier operation. The SCell may be setup or released in the downlink, uplink, or both. Examples of commands that the network can use in the multi-carrier SCell setup procedure include Configuration of SCell(s), De-configuration of SCell(s), Activation of SCell(s), and Deactivation of SCell(s).
The configuration procedure is used by the serving radio network node (e.g., eNode B in LTE) to configure a carrier aggregation capable wireless communication device with one or more SCells in the downlink, uplink, or both. The de-configuration procedure is used by the serving radio network node to de-configure or remove one or more already configured SCells in the downlink, uplink, or both. The configuration or de-configuration procedure can also be used to change the current multi-carrier configuration. For example, the number of SCells can be increased or decreased, or existing SCells can be swapped with new ones.
The serving radio network node can activate one or more deactivated SCells or deactivate one or more SCells on the corresponding configured secondary carriers. The PCell is always activated. The configured SCells are initially deactivated upon addition and after a cell change, such as a handover. In LTE, the activation and deactivation command is sent by the eNode B via a media access control—control element, MAC-CE. The deactivation of SCell saves the wireless communication device's battery power.
The SCell activation delay requirements are defined in TS 36.133 release 10. According to which, upon receiving SCell activation command in subframe n, the wireless communication device shall be capable to transmit a valid channel state information, CSI, report and apply actions related to the activation command for the SCell being activated no later than in subframe n+24 provided the following conditions are met for the SCell: 1) during the period equal to max(5 measCycleSCell, 5 DRX cycles) before the reception of the SCell activation command, (a) the wireless communication device has sent a valid measurement report for the SCell being activated, and (b) the SCell being activated remains detectable according to the cell identification conditions, and 2) the SCell being activated also remains detectable during the SCell activation delay according to the cell identification conditions. Otherwise upon receiving the SCell activation command in subframe n, the wireless communication device shall be capable to transmit a valid CSI report and apply actions related to the activation command for the SCell being activated no later than in subframe n+34 provided the SCell can be successfully detected on the first attempt.
The SCell deactivation delay requirements are also defined in TS 36.133 release 10. According to which, upon receiving SCell deactivation command or upon expiry of the sCellDeactivationTimer in subframe n, the wireless communication device shall accomplish the deactivation actions for the SCell being deactivated no later than in subframe n+8.
Certain wireless communication devices capable of SCell operation may also be capable of device-to-device, D2D, operation. Although the PCell and the SCells are primarily used for WAN operations, such as the reception and/or transmission of cellular signals, D2D capable wireless communication devices can be configured for D2D operation on PCell and/or on one or more SCells.
A D2D wireless communication device transmits D2D signals or channels in the uplink part of the spectrum. D2D operation by a wireless communication device is in a half-duplex mode, meaning that the wireless communication device can either transmit D2D signals/channels or receive D2D signals/channels. There may also be D2D relay wireless communication devices that may relay some signals to other D2D wireless communication devices.
Certain control information for D2D operation may be transmitted by D2D wireless communication devices. Other control information may be transmitted by radio network nodes. For example, D2D resource grants for D2D communication may be transmitted via cellular downlink control channels. The D2D transmissions may occur on resources which are configured by the network or selected autonomously by the D2D wireless communication device.
D2D communication implies that a D2D transmitter transmits information to assist D2D receivers in receiving D2D data. The information includes the D2D data and D2D communication control information with scheduling assignments. The D2D data transmissions are according to configured patterns and in principle may be transmitted rather frequently. Scheduling assignments are transmitted periodically. D2D transmitters that are within the network coverage may request eNodeB resources for their D2D communication transmissions and receive in response D2D resource grants for scheduling assignments and D2D data. Furthermore, the eNodeB may broadcast D2D resource pools for D2D communication.
D2D discovery messages are transmitted in infrequent periodic subframes. The eNodeBs may broadcast D2D resource pools for D2D discovery, both for reception and transmission.
The D2D communication supports two different modes of D2D operation: mode 1 and mode 2. In mode 1, the location of the resource for transmission of the scheduling assignment by the broadcasting wireless communication device comes from the eNodeB. The location of the resource(s) for transmission of the D2D data by the broadcasting wireless communication device also comes from the eNodeB. In mode 2, a resource pool for scheduling assignment is pre-configured and/or semi-statically allocated. The wireless communication device on its own selects the resource for scheduling assignment from the resource pool.
When the wireless communication device switches its reception from D2D reception to wireless access network, WAN, reception (e.g., cellular network reception) or from WAN reception to D2D reception, PCell interruption of 1 subframe occurs. This is because the wireless communication device receiver chain needs to be retuned every time the operation is switched from WAN to D2D reception and from D2D to WAN reception. This applies to both D2D discovery and D2D communication capable wireless communication devices.
It is important to partition resources between uplink cellular and D2D and to schedule the wireless communication device for WAN and D2D in such a way that avoids or minimizes the risk of switching taking place in certain subframes. For example, in LTE subframe #0 and/or subframe #5 of the PCell contain essential information, such as primary synchronization signals, PSS, and secondary synchronization signals, SSS, that are necessary for doing cell searches and carrying out cell measurements. The subframes also contain master information block, MIB, and/or system information block 1, SIB1, information which is necessary for system information reading procedures.